This invention is directed to novel processes for the restoration of teeth, especially posterior teeth. Certain practical considerations apply to the formulation and application of resin based posterior dental restoratives. Accordingly, it is greatly preferred that the restorative composition be effectively homogeneous such that air bubbles or structural discontinuities are substantially avoided from introduction into tooth structure. Additionally, it is greatly preferred that such materials be "packable" and be capable of deforming a matrix band during the course of tooth filling. Such material must also be capable of withstanding the physical stresses extant in the posterior region of the mouth and not crumble, fracture, or erode under such conditions.
It has long been known to employ metallic amalgams in the restoration of posterior teeth. Such amalgam materials have been shown to have good resistance to the physical stresses experienced by posterior teeth and to possess small coeffecients of thermal expansion. Such amalgams have also been demonstrated to have good "packability" and to demonstrate other properties necessary of the posterior restorative. Such materials, however, suffer from uncertainty as to the biological effect of introduction of mercury and other metals in the oral cavity over long periods of time. Additionally, the metallic hue of such restorations is a significant aesthetic detriment.
United Kingdom application GB 2,028,855 published Mar. 12, 1980 discloses a posterior restorative based upon a poly(carboxylic acid) system. Several additional resin based restorative compositions have been proposed for use in the filling of posterior teeth; each of these has demonstrated one or more shortcomings which render them ineffective for such use. Those restorative compositions which have been offered for use in posterior restoration are believed to show substantial physical degradation in use within a relatively short period of time, i.e., about two years, and, accordingly, to be unsuitable for such posterior restorative use. Additionally, such materials are self-curing (autocatalytic), two component systems which require manual mixing prior to use. Such mixing is poorly suited to the attainment of good homogeneity of a restorative since mixing tends to incorporate air into the restorative leading to voids in the restoration and lack of durability.
Those skilled in the art of dental restoration will appreciate that certain posterior restorations, such as Class II restorations, require the employment of a matrix for proper application. Thus, it will be appreciated that the use of a matrix band to surround a tooth to be repaired is generally necessary. More particularly, such bands are needed when the tooth to be repaired must be excavated in such a fashion that the resulting cavity preparation communicates from the top surface to one or more of the side surfaces of the tooth. In such a case, the matrix band is placed around the tooth and held tightly in place while restorative such as amalgam is put into place. The packability of conventional dental amalgams is described, for example, in U.S. Pat. No. 4,226,622 which is incorporated herein by reference.
In interproximal restorations, it is considered vital to so configure the restoration as to attain contact between the restored tooth and the neighboring tooth. Contact is needed for self-cleaning and the avoidance of malocclusion. Such contact has traditionally been attained by contouring the matrix prior to filling with amalgam. Furthermore, amalgam has been packed into the cavity preparation in such a way as further to deform the matrix to ensure the attainment of the original tooth contour and contact with adjacent teeth when appropriate. The foregoing resin based restoratives are not generally capable of being compacted to a degree sufficient to deform a matrix band according to preferred practice. Accordingly, there has been a long felt need for materials and processes for one component resin-based posterior restoration which permits matrix band deformation in practice. Also, there has been a long felt need for resin-based restorative materials which are packable, which eliminate voids and gaps in a restoration, and which better conform to irregularities in the walls of the cavity preparation.